Hi,

I have a question about TEC controller ADN8834.

I can see an equation of f_0dB in DS at p18.

Can you explain what TECGAIN in it?

from Fig 35, 0dB should be at 1/(2*pi*R_1*C_1). But f_0dB of equation has x(R_FB/(R_TH + R_x) - R_FB/R)xTECGAIN.

I assume the followings;

1. TECGAIN is a varied value from device itself. It can change by hot mode or cold mode.

2. When users think of PID Compensation, they can ignore x(R_FB/(R_TH + R_x) - R_FB/R)xTECGAIN. The part would be canceled as x1 or very tiny???

Is my assumption correct?

If not, could you explain what it is?

I would like to know

- What is TECGAIN? and how can it be led in calculation?

- Why is x(R_FB/(R_TH + R_x) - R_FB/R)xTECGAIN ignored in Fig 35?

Thank you for your help.

The feedback circuitry is composed of the thermistor amplifier and the PID compensator, which are named as Chopper 1 and Chopper 2 respectively on page 18 of the DS. Chopper 1 takes the feedback voltage from the thermistor and its transfer function is (R_FB/(R_TH + R_x) - R_FB/R). Since Fig. 35 is illustrating the Bode Plot of PID compensator (Chopper 2), Chopper 1 is not presented in it.

TECGAIN is a term used to describe all other factors in the thermal feedback loop including thermal resistance, material coefficient of the TEC itself, and the module case or heat sink that might potentially exist. These parameters vary case by case and are too complicated to be modeled mathematically. Thus TECGAIN here is not used for calculation but for showing why PID online tuning is the preferred method to design the compensator.